Look at who makes minimum wage. Typically it's service jobs. Will Walmart have fewer cashiers? Will McDonald's? If that happens waits go up. If that happens then people stop going to those stores and start going where waits aren't as long - companies like Costco that have no issue paying a higher wage to their employees.

Many of the people that are against raising minimum wage are the same that love saying things like "the market will take care of it." Well, the market would also make sure that companies keep their staffing levels. It isn't as if Walmart or McDonald's are employing more people now than they need - they run close to the bare minimum. They can't simply employee fewer people without utterly destroying the experience to their own detriment.